White sweetclover (Melilotus albus) was introduced as early as 1664 as a forage crop. Since then white sweetclover has naturalized throughout most all of North America. Also used for soil stabilization and improvement, white sweetclover has become an invasive weed in some areas because of its ability to out-compete with native plants. Today white sweetclover can be found along roadsides, in cultivated fields and other disturbed places, where it is often the first plant to appear.
White sweetclover is a sweet-smelling annual or biennial, although occasionally perennial growth has been reported. White sweetclover is not a true clover (Trifolium) but rather belongs to the pea or legume family and as such can fix nitrogen in the soil. Among its many common names are honey clover and white melilot.
Arising from a taproot, the erect, branching white sweetclover stems can grow up to seven feet in height. Small fibrous roots with nitrogen-fixing microbial nodules spread out from the plant’s main tap root. The leaves are compound with three toothed, lance to oval shaped leaflets. The numerous white, pea-like flowers are crowded in spike-like racemes (clusters). The seeds are contained in hairless pods with a veined surface which turn black when mature. Seeds are dispersed by animals and by transport of contaminated hay and feed. The smooth seeds can float and are also spread by water.
The sweet odor of M. albus is caused by coumarin, which under certain natural conditions can prevent the clotting of blood. For this reason white sweetclover is often used in homeopathic medicine to improve blood circulation. Livestock eating large quantities of white sweetclover can become prone to excessive bleeding even with minor injuries. Cattle can also bloat on sweetclover.
In some areas white sweetclover is an important source of nectar for honeybees as well as other insects.
Yellow sweetclover (Melilotus officinalis) looks very similar to white sweetclover with flower color (white versus yellow) being the most obvious difference. Often these two species are sometimes classified together as M. officinalis, yet they do not appear to be genetically compatible and for now probably should remain as separate species.
These white sweetclover plants were photographed in McArthur Swamp (Shasta County CA).